Over the past several decades, the Northeast has experienced a strong increase in the frequency and intensity of extreme precipitation events.22 Regional increases in heavy precipitation events exceed that of the rest of the United States with a 74% increase in the heaviest 1% of all precipitation events since 1958. Flood events have risen in association with increases in precipitation, particularly extreme events. This puts fish, wildlife, and their habitats at increased risk to direct impacts, such as physical damage, displacement, and mortality, as well as indirect impacts that result from increased inputs of sediments, nutrients, and pollution to aquatic systems.

The largest increases in heavy precipitation extremes are projected to occur in the northern, coastal, and mountainous areas of the region.20 Some locations in Massachusetts, such as the eastern region, have shown an increasing trend in the number of days with two inches of precipitation or more since 1970.5,13 Annual maximum daily precipitation (the maximum amount of precipitation that fell within a 24-hour period over the course of a year) in coastal Massachusetts and the greater northern New England region has also increased by 1 to 2 inches since 1970.5 In addition, the Connecticut River basin has experienced more than a doubling of heavy rainfall events over the last 60 years. Regionally, the majority of heavy precipitation events have occurred during the summer months of May through September.

Coastal Storms
Changes in the frequency and intensity of coastal storms and the interactive effects with sea level rise increases the vulnerability of coastlines and coastal habitats to these natural hazards.

Severe Thunderstorms, Tornados, and Hail Events
Thunderstorms and other severe weather pose threats to fish and wildlife habitats through structural damage to trees, as well as erosion and riparian bank washout events. There is relatively less and sometimes conflicting information on observed and projected trends in storms compared to other areas of climate science, making it difficult to predict how these events may change in the future. Some evidence suggests the number of tornadoes per year has not changed much regionally since 1970. In the United States as a whole, there is some evidence that the number of days with tornadoes is decreasing, although the number of tornadoes per day may be increasing. Increased warming due to climate change could increase the frequency of severe storms that include tornadoes, damaging wind, and hail, particularly in the summer. Future studies in this area are needed to improve our understanding of the impact of climate change on severe storms and their impacts on natural resources.

The 100-year flood event (a flood of magnitude that occurs on average once every hundred years) is now occurring every 60 years on average, when rainfall amounts from 1978-2007 are compared with 1950-1979. For much of the Atlantic Coast, 100-year flood events are projected to occur every 10-20 years by the year 2050.17,19 In addition, the 50-year flood is now occurring approximately every 30 years. By 2100, Boston’s current 100-year coastal flood event is projected to recur every 1-2 years, on average, and increase in height from nearly 10 feet to more than 12 feet under a high emissions scenario.8 In Woods Hole, MA, 100-year floods are expected to recur every 9 years, on average, under a high emissions scenario and every 21 years under a low emissions scenario.8

Future projections show that extreme precipitation events are very likely to continue to intensify during all seasons. Coastal Massachusetts is particularly at risk to extreme precipitation events with the interacting effects of coastal storms and sea level rise. In addition, these events are expected to become more numerous in Massachusetts, as well as the greater Northeast region, though with greater year-to-year variability.

Winter Storms
Winter storms, such as blizzards and ice storms, are occurring more frequently in the Northeast and Massachusetts. Severe snow and ice storms have more than doubled over the last 55 years relative to the previous 60 years. However, more precipitation is falling in the form of rain than snow. The impacts of winter storms vary and may be localized to particular areas of the State. Nor’easters (discussed on the Coastal Storms page) are a major driver of winter storms in Massachusetts, and observational evidence suggests that these phenomena are becoming more intense and occurring more often in New England overall than in the past.

3. Colle, B. A., K. Rojowsky, and F. Buonaito. 2010. New York City Storm Surges: Climatology and an Analysis of the Wind and Cyclone Evolution. Journal of Applied Meteorology and Climatology 49:85-100.

15. Kunkel, K. E. 2013. Regional climate trends and scenarios for the US National Climate Assessment. US Department of Commerce, National Oceanic and Atmospheric Administration, National Environmental Satellite, Data, and Information Service.